Development of tumors in the glandular stomach of rats after oral administration of carcinogens. I. Histological findings

Effect of N-methyl-N'-nitro-N-nitrosoguanidine on carbohydrate profiles of non-metaplastic rat gastric mucosa

The effect of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) on the mucin phenotype of non-metaplastic gastric mucosa in the rat was studied histochemically. Animals were exposed to MNNG in drinking water (83 mg/l) for 12 weeks. Carcinogen treatment was then discontinued and the animals (27 in the treatment group and 25 in the control group) were examined after another 44 weeks. Glycosylation was analysed with histochemical stains for sialomucins and sulphomucins and with peroxidase-conjugated lectins (GS-II, SBA, DBA, UEA-I, and WGA). Sialo- and sulphomucins remained quantitatively unchanged, only a slight increase of acid mucins in the antral glands was observed. The analysis of the lectin binding patterns, however, revealed a significant increase for WGA-binding glycoproteins in the surface mucous cells and gastric pits, while DBA binding was significantly decreased (P < 0.05). GS-II lectin bound specifically to the proliferative compartment in the gastric fundus, consisting of mucous neck cells, and was significantly increased after MNNG treatment. No specific alterations were detected in lectin binding to parietal or chief cells. It is concluded, therefore, that treatment of gastric mucosa with MNNG alters the glycoprotein metabolism before intestinal metaplasia can be observed.

Gastric carcinogenesis: a model for the identification of risk factors

In a series of extensive studies on gastric carcinogenesis, we have used Sprague-Dawley rats to examine the morphologic, histochemical, and biochemical effects of risk and protective factors on N-methyl-N'-nitro-N-nitroso guanidine (MNNG)-induced tumors in an attempt to link early observations with the end-point lesion, gastric cancer. We have observed that the putative risk factors sodium chloride (NaCl); a mixture of bile acids; aspirin; alcohol; and nitrite enhance MNNG-induced neoplasia of the gastric mucosa. On the other hand butylated hydroxyanisol (BHA), Se and difluromethylornithine (DFMO) were protective and inhibited the induction of gastric mucosal neoplasia. In most cases, early changes detected by a number of criteria correlated with the end-point, gastric neoplasia. This model appears to be useful in screening and evaluating chemicals for risk for or protection against gastric cancer.

The effects of different MNNG (N-methyl-N'-nitro-N-nitrosoguanidine)-doses on the stomach and the upper small intestine of the rat. II. The frequency of intestinal metaplasia

N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) was given to 3 groups of male Wistar rats in different doses of 25 micrograms/ml, 50 micrograms/ml and 100 micrograms/ml with their drinking water for 32 weeks. After 50 weeks the antrum region of the stomach was investigated by serial sections. All animals showed tubules with metaplastic intestinal epithelium. The different values of metaplastic glands in the antrum region of the stomach were 187 (25 micrograms MNNG), 76 (50 micrograms MNNG) and 51 (100 micrograms MNNG). They indicate an inverse relationship of the frequency of intestinal metaplasia and the MNNG dose. As opposed to this dose-response pattern, cytotoxic alterations, regenerative hyperplastic lesions and tumours of the stomach are more frequent after medium of high MNNG doses. It is therefore suggested that the induction of intestinal metaplasia is a specific effect of the carcinogen mainly in the low dose range.

Chemical carcinogens. A review and analysis of the literature of selected chemicals and the establishment of the Gene-Tox Carcinogen Data Base. A report of the U.S. Environmental Protection Agency Gene-Tox Program

The literature on 506 selected chemicals has been evaluated for evidence that these chemicals induce tumors in experimental animals and this assessment comprises the Gene-Tox Carcinogen Data Base. Three major sources of information were used to create this evaluated data base: all 185 chemicals determined by the International Agency for Research on Cancer to have Sufficient evidence of carcinogenic activity in experimental animals, 28 selected chemicals bioassayed for carcinogenic activity by the National Toxicology Program/National Cancer Institute and found to induce tumors in mice and rats, and 293 selected chemicals which had been evaluated in genetic toxicology and related bioassays as determined from previous Gene-Tox reports. The literature data on the 239 chemicals were analyzed by the Gene-Tox Carcinogenesis Panel in an organized, rational and consistent manner. Criteria were established to assess individual studies employing single chemicals and 4 categories of response were developed: Positive, Negative, Inconclusive (Equivocal) and Inconclusive. After evaluating each of the individual studies on the 293 chemicals, the Panel placed each of the 506 chemicals in an overall classification category based on the strength of the evidence indicating the presence or absence of carcinogenic effects. An 8-category decision scheme was established using a modified version of the International Agency for Research on Cancer approach. This scheme included two categories of Positive (Sufficient and Limited), two categories of Negative (Sufficient and Limited), a category of Equivocal (the evidence of carcinogenicity from well-conducted and well-reported lifetime studies had uncertain significance and was neither clearly positive nor negative), and three categories of Inadequate (the evidence of carcinogenicity was insufficient to make a decision, however, the data suggested a positive or negative indication). Of the 506 chemicals in the Gene-Tox Carcinogen Data Base, 252 were evaluated as Sufficient Positive, 99 as Limited Positive, 40 as Sufficient Negative, 21 as Limited Negative, 1 as Equivocal, 13 as Inadequate with the data suggesting a positive indication, 32 as Inadequate with the data suggesting a negative indication, and 48 Inadequate with the data not suggesting any indication of activity. This data base was analyzed and examined according to chemical class, using a 29 chemical class scheme.(ABSTRACT TRUNCATED AT 400 WORDS)

[Histoautoradiographic studies of Billroth I-operated rat stomachs in relation to the postoperative interval. II. Histologic changes in the area of the anastomosis and its proliferation-kinetic behavior]

In a postoperative interval of 104 weeks' experience with 75 Wistar rats resected according to Billroth's 1st principle, the fourfold of standard of proliferative activity in addition to extended displacements and decompositions could be demonstrated. During 104 weeks of experience 8 animals developed in the anastomosed mucosa section adenomatous cystic glandular proliferations, 5 animals anastomotic polypi, 16 animals dysplastic gland areas and 10 animals showed anastomotic carcinomas. For these pathologic-anatomically outlined changes cellular proliferation was analysed by histoautoradiographic methods in parts of highest mitotic activity. The results were interpreted in dependence on their postoperative interval. In all pathologic-anatomical changes sources of strongest labelling could be found in the periphery. As most serious complication rats in experiment developed carcinoma in the anastomosed parts of mucosa. The peripheral sections of the carcinoma, so-called "front of invasion", showed regions of highest mitotic activity. Analysis of histoautoradiographic investigation in pathologic-anatomical change revealed modified proliferation kinetics in the sense of highly increased cell proliferation rates, which refer to the important role of the anastomotic region in the resected stomach.

Three-dimensional morphological study of rat gastric lesions induced by N-methyl-N'-nitro-N-nitrosoguanidine. Structural atypia in carcinoma and non-carcinomatous lesions

Lesions of the rat glandular stomach induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) were classified into 4 categories: intramucosal lesions; polypous lesion; downward-growth lesions, and unequivocal adenocarcinomas. Each lesion was examined by three-dimensional reconstruction from serial sections to study the spacial arrangement of the glandular tubules. In the intramucosal lesions, the tubules showed tree-like branchings. In the polypous lesions and downward-growth lesions, the tubules were interconnected to form a three-dimensional network. In unequivocal adenocarcinomas, the tubules appeared separated and were dispersed into nests. These findings indicate that interruption of continuity of the epithelium in proliferated tubules is a possible sign of malignant transformation. Erosions were always observed in the intramucosal, the polypous and the downward-growth lesions. There were locations in the tubular system where the tubules became so attenuated as to resemble cord like structures. Inflammatory reactions were always demonstrable in the intertubular spaces in such lesions. These findings indicate that MNNG-induced anatomical changes may participate in the formation of erosions by causing local obstruction of the ductules.

Genetic effects of N-methyl-N'-nitro-N-nitrosoguanidine and its homologs

Since the discovery of the mutagenic activity of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) in 1960, this compound has become one of the most widely used chemical mutagens. The present paper gives a survey on the chemistry, metabolism, and mode of interaction of MNNG with DNA and proteins, and of the genotoxic effects of this agent on microorganisms, plants, and animals, including human cells cultured in vitro. Data on the carcinogenicity and teratogenicity of MNNG as well as on the genotoxic effects of homologs of MNNG are also presented.

Induction of carcinoids in the glandular stomach of rats by N-methyl-N'-nitro-N-nitrosoguanidine

A total of 30 inbred Wistar rats were orally administered 70 microgram/ml solution of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) for 35 weeks and then tap water for the following 20 to 30 weeks. Four of the 20 females and two of ten males developed carcinoids in the glandular stomach, but no metastasis could be found. Carcinoids developed most frequently in the fundic portion along the greater curvature. Histologically, these tumors were medullary anaplastic carcinomas containing two different endocrine cell populations. The first cell type was argentaffin having the electron-dense, somewhat pleomorphic secretory granules (437-810 nm) and the second type was argyrophil having round granules with a dense core and a pale halo (550 nm). None of these tumors showed endocrine immunoactivity for gastrin, somatostatin, insulin, glucagon, and enkephalin. One of these gastric tumors developed into scirrhous carcinoma, but differentiated adenocarcinoma could not be seen in the glandular stomach.

Early sequential lesions during development of experimental gastric cancer with special reference to dysplasias

The early sequential development of gastric cancer was studied with experimental animals and examined with respect to what conclusions can be drawn for understanding carcinogenesis in man. After limited oral administration of N-methyl-N'nitro-N-nitrosoguanidine to 174 rats carcinomas developed in most cases directly from the otherwise unchanged mucosa through various successive stages of transformation, without passing through a benign-appearing proliferative or neoplastic epithelial lesion. Focal dysplasia grade I was the first recognizable change observed by light microscopy, followed by dysplasia grade II, and subsequently dysplasia grade III. In spite of very similar morphological characteristics, the experimentally induced dysplasias cannot be simply equated in their etiology and biological behavior with the dysplasias of the human stomach. Dysplasias of grade I and II commonly found in man are usually associated with a chronic gastritis; they are located in the upper third of the mucosa and are for the most part reversible. The experimental dysplasias occuring in the proliferative zone of an otherwise undisturbed mucosa must be considered potentially premalignant, as they are irreversible and develop progressively. This finding points out that in man dysplasias grade III within the regenerative zone of non-inflammatory mucosa should be considered particularly as possible precursors of gastric carcinomas.

A mode of incipient growth in chemically induced signet ring cell carcinoma of the canine stomach

A 31-month-old female mongrel dog was orally administered with 50 mg or 100 mg of N-nitrosobutylurea (NBU) in gelatin-capsule 3 times per week for 19 months with interposing periods of complete suspension. Thirty-four foci of signet ring cell carcinoma were found in the antral region of the stomach. The majority of the foci (31 foci) were early cancer, and the remaining foci were invasive cancer. In addition to these lesions, there was "a single gland cancer" in which a row of cancer cells was confined to a single gland. The whole gland was composed of two cell layers; the inner layer facing the lumen was normal gastric cells and the outer layer was atypical or neoplastic cells underlaid by the basement membrane. Mitosis was frequently observed on the bottom of the gland. Atypical or neoplastic cells seemed to mature gradually through a process of upward migration with increase in cytoplasmic Alcian blue-PAS and HID-AB positive mucin. Some of the cells rich in mucin moved into the lamina propria. The other cells remained in the flow of the regular cell renewal system of the normal gastric cells and reached the top of the gland. This observation revealed a mode of incipient gastric cancer growth, which starts and spreads within a single gland, before it invades the surrounding lamina propria.

Development of tumors in the glandular stomach of rats after oral administration of carcinogens. II. Different cell types in antral carcinoma as revealed by electron microscopy

In the present study electron microscopic investigations of tumors of the glandular stomach of rats induced by oral administration of MNNG or ENNG are dealt with. The aim of the study was to describe the different cell types found in the carcinoma and to elucidate the possible relationship between the undifferentiated carcinoma cells and the more differentiated cell types found in the tumor. The results show that besides undifferentiaded carcinoma cells, several differentiated cell types such as goblet cells, endocrine cells, cells with lamellated inclusions in their cytoplasm, and squamous carcinoma cells can be observed. The most conspicuous findings were carcinomatous gland cells with well differentiated microvilli on their luminal surface and typical tonofilamentous structures in their cytoplasm. These cells exhibited signs of the squamous epithelium and of gland cells. Therefore they may be considered as intermediate variants between adenocarcinoma cells and squamous carcinoma cells. The occurrence of such intermediate steps points to the possibility of differentiation by cell division of adenocarcinoma cells into several metaplastic cell types in the experimental stomach carcinoma induced by MNNG or ENNG.